Problem with pinging broadcast address

networking broadcast ping icmp

10,655

Solution 1

Some hosts simply don't respond to broadcast pings (for example, Windows is configured by default this way).

Solution 2

Because in example some implementations work by sending the broadcast to the preferred interface, not all of them. You need a relay to send to all interfaces. You may consider reading the RFC 919

10,655

Author by

pflz

Updated on June 04, 2022

Comments

pflz almost 2 years

When I try to ping the broadcast address on my LAN, it shows ICMP replies from only 3 hosts, everytime, even though there many hosts connected to the LAN.

For the broadcast address, I did

$ifconfig eth0
eth0      Link encap:Ethernet  HWaddr 00:1b:38:09:0b:26  
          inet addr:172.30.120.152  Bcast:172.30.127.255  Mask:255.255.248.0
          inet6 addr: fe80::21b:38ff:fe09:b26/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:831096 errors:0 dropped:0 overruns:0 frame:0
          TX packets:13022 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:66620362 (66.6 MB)  TX bytes:3099025 (3.0 MB)
          Interrupt:21 Base address:0x2000

I used the Bcast addr 172.30.127.255 to ping everyone...

$ping -b 172.30.127.255
WARNING: pinging broadcast address
PING 172.30.127.255 (172.30.127.255) 56(84) bytes of data.
64 bytes from 172.30.120.1: icmp_seq=1 ttl=255 time=0.809 ms
64 bytes from 172.30.120.62: icmp_seq=1 ttl=64 time=1.06 ms (DUP!)
64 bytes from 172.30.120.50: icmp_seq=1 ttl=255 time=3.97 ms (DUP!)
64 bytes from 172.30.120.1: icmp_seq=2 ttl=255 time=0.364 ms
64 bytes from 172.30.120.62: icmp_seq=2 ttl=64 time=0.412 ms (DUP!)
64 bytes from 172.30.120.50: icmp_seq=2 ttl=255 time=1.48 ms (DUP!)
64 bytes from 172.30.120.1: icmp_seq=3 ttl=255 time=0.452 ms
64 bytes from 172.30.120.62: icmp_seq=3 ttl=64 time=0.506 ms (DUP!)
64 bytes from 172.30.120.50: icmp_seq=3 ttl=255 time=1.64 ms (DUP!)

Why is that only 3 hosts respond to my ping. Is this bcast address given by ifconfig not the one to be used? I think this might be the reason why I am not able to carry out an amplification attack on a system on my LAN. I injected ICMP-echo packets with spoofed source address of my friend's host and sent it to this broadcast address, and was disappointed to see that his bandwidth was not affected...

Kindly explain...